Non-contact measurement of surface velocity can be done using an optical interference method and sensing the Doppler shift of reflected light from a target. If the target vibration is to be measured, the reflected light acquires a spectrum of sidebands from the range of vibrational frequencies at the target. This type of measurement differs in many details from that of a static, or quasi-static, velocity measurement such as in laser radar, or measurement of atmospheric aerosol velocities, although both rely on the same basic physical principles. In this specification, the invention is applied to measurement of small-amplitude, acoustic-frequency surface vibrations, but is also applicable to special cases of non-periodic velocities as well.